Illumination devices are often utilized for lighting subject matter in television broadcasting and/or for recording on film, video, digital storage, cinema, video, photography etc. Such illumination devices will herein be referred to as “studio lighting” sources. Studio lighting sources may be divided into two general categories: (1) hard and (2) soft. Hard lighting usually is associated with undiffused, direct light (for example, from a lamp in a light fixture) which may act as a point source of light, where the light rays striking the intended subject predominantly come from a single direction and cause pronounced shadows, highlights and contrast. Soft lighting usually refers to diffused light source that appears to “wrap” around objects, casting shadows with soft edges, and lowering the contrast and highlights. Light rays from a lamp or reflector may be softened when they pass through diffusive material and/or undergoing multiple reflections within the diffusive material. By directing the light rays to spread out in many directions, the diffusive material may subsequently act to create multiple point sources, or effectively extend the area of the source such that light rays are incident on the intended subject from a greater number of angles, producing less shadows, highlights and contrast. It is this second category of soft light sources that the present disclosure relates to.
An important consideration in studio lighting is the ability to control the type and placement of the light fixture so that the output properly lights the scene. For example, a scene on a movie set may require lighting subjects such as people, objects, areas, etc. and each of the subjects may have their own respective lighting requirements. Certain lighting situations may require “fill” lighting where one or more light fixtures with broad light dispersion patterns illuminate the entire location area. However, there are proportionally more situations that require the light to be directed towards specific subjects, and not to “spill” onto unwanted areas. Examples of light fixtures used for this purpose include fixtures that use parabolic reflectors, light grids, or louvers that partially collimate the light, and attachments such as “barn door” flaps that can control the light spillage from the fixture.
Generally, soft lighting devices fall into two general categories: (a) soft studio light sources and (b) traditional softboxes. The first category (soft studio light sources) includes light fixtures in which the output light is directed through a diffusive translucent material before reaching the subject. Such fixtures generally include an open face enclosure with a lamp disposed in front of some type of rear reflector and a diffusive material mounted in some manner on the fixture's front frame. This type of soft studio light source can suffer from a number of drawbacks, including but not limited to:
a) The fixtures are generally designed to function as partial light collimators, and not as dedicated diffusion boxes. For example, the fixtures typically have curved mirrored or metallic reflectors disposed behind the light source as a means to collimate or condense the illumination pattern to some degree. The diffusive material may be mounted in some fashion on the front face of the light fixture directly on the front of the light source. For example, a gel frame may slide into tracks disposed on the front face of the fixture. Due to the close proximity of the diffusion material to the partially collimated light source and the lack of light scattering within the fixture, the output luminance across the diffusion material may be non uniform, and may exhibit distinct “hot spots” in the areas directly in front of the lamps, and may result in an uneven illumination pattern.
b) The backscatter of light reflecting from the back side of the diffusion material may be lost or absorbed either through the space between the diffusion material and frame of the fixture or from absorption losses within the enclosure. Such absorption or misdirection of the light can reduce the efficiency of the fixture.
c) The light output from the diffusion material may exhibit a very wide dispersion pattern. In order to narrow this dispersion pattern as required for a particular lighting setup, light blocking or honeycomb grids may typically be placed in front of or behind the diffusion material, and narrow the beam by blocking, absorbing, or reflecting light rays that fall outside a desired coverage angle. Light energy absorbed by the grids may therefore, wasted. The deeper and the narrower the grid channels, the narrower the beam and the greater the light loss. By this very nature, grids are a very inefficient means for controlling the direction of light, and they incur large losses of light intensity.
d) Light fixtures that utilize linear fluorescent lamps typically have reflectors disposed directly behind the lamps and such reflectors have a degree of curvature to collimate the reflected light to some extent. This curvature, necessitated by the linear geometry of the fluorescent lamp, is generally in a single direction following the major axis of the lamp. Accordingly, the dispersion pattern of the light will only be condensed in a plane perpendicular to the major axis of the lamps. For example, if the lamps are disposed in a horizontal direction, the light output pattern will be condensed in the vertical direction.
e) Light fixtures typically have fixed reflectors that collimate the light to a predetermined viewing angle. Changing this viewing angle may necessitate the use of diffusion material to spread the pattern, or grids or louvers to collimate the light further.
f) Light fixtures with “hot” lights such as sodium, tungsten, hydrargyrum medium-arc iodide (HMI) etc, typically use rear parabolic reflectors; however, such fixtures are very bulky and large. Generally, the more efficient the reflector, the more parabolic in shape it will be, with a corresponding increase in depth of the reflector and light fixture.
g) A typical studio light with fluorescent lamps relies on ventilation through the front face of the unit. Such fixtures typically utilize a gel frame for attaching the diffusion material. The gel frame usually slides or clips onto suitable holders on the front frame of the unit. Subsequently, inadequate space is sometimes left between the face of the unit and the light modifying films, restricting air flow around the lamps. Such restriction of air flow can reduce life expectancy and can cause the high output lamps to increase their operating temperature, which can increase the color temperature and the green spectrum of the light output.
The second category of soft lighting devices (as referred-to above) are diffusion enclosures or “traditional softboxes.” A traditional softbox, as illustrated in FIG. 7a, is an enclosure with a generally parabolic shape, a light source disposed therein, reflective walls, an optional translucent diffusing sheet (typically white nylon fabric) suspended midway in the softbox for extra light reflection and diffusion, and a layer of the same diffusion material at the light output end of the enclosure. The enclosure is usually formed by stretching a vinyl or nylon fabric over a heavy wire frame. Inside the softbox, the walls are typically lined with a reflective material such as an aluminized fabric, foil, or white vinyl. There are numerous permutations of this basic design, but most all have walls designed to act as basic reflectors that cause light output from the source lamp to undergo multiple reflections within the softbox, and to direct light rays forward towards the diffusion layer at the light output end of the softbox. These multiple reflections serve to scatter the direct light from the lamp, thus “mixing” the light within the softbox, creating a more uniform luminance output pattern. While traditional softboxes often do create an adequately diffused output surface for many applications, they suffer from a number of drawbacks, some of which are:
a) They tend to be bulky. For example, a typical 32″×44″ softbox could have a depth on the order of 26″ in order to achieve the required diffusion.
b) Because of their structural properties, they generally only accept a single or small grouping of point source type lamps, and are not able to accommodate linear type fluorescent lamps.
c) The light loss can be substantial due to inefficiencies in reflective materials and enclosure design. Losses can also occur when the light passing through layers of inefficient diffusive material, such as translucent nylon fabric.
d) Traditional softboxes are designed to maximize the diffusion of the light source, and therefore, the output light dispersion pattern can be extremely wide. Restricting the diffused light output pattern to a particular region within a scene has traditionally required attaching bulky and cumbersome light absorbing or blocking louvers to the face of the softbox. Such methods add additional unwanted depth to the softbox, and they usually fail to provide a substantially tight output light dispersion pattern.
e) They have no means to incorporate a ventilation system capable of adequately maintaining the internal operating temperature within acceptable limits when a sufficient number of high output, high wattage lamps are used. Therefore, temperatures can rise above optimum levels and can cause a change the color temperature or color balance of the output light, and can decrease the lamp life expectancy.
f) Attaching light modifying films to the front face is a cumbersome and time-consuming process.
There are many drawbacks associated with existing studio soft lights and traditional softbox designs. A need remains for improved systems and apparatus that can provide an improved light diffusion and condensing fixture.